Effects of Ocean Acidification and Flow on Oxygen and pH Conditions of Developing Squid (Doryteuthis pealeii) Egg Cases

While young animals found future cohorts and populations, these early life stages are often particularly susceptible to conditions of the local environment in which they develop. The oxygen and pH of this critical developmental environment is likely impacted by the nearby physical conditions and the animals own respirations. Yet, in nearly all cases, this microenvironment is unknown, limiting our understanding of animal tolerances to current and future OA and hypoxic conditions. This study investigated the oxygen and pH environment adjacent to and within the egg cases of a keystone species, the longfin squid, Doryteuthis pealeii, under ambient and elevated CO₂ (400 and 2200 ppm), and across differing water flow rates (0, 1, and 10 cm/s) using microprobes. Under both CO₂ treatments, oxygen and pH in the egg case centers dropped dramatically across development to levels generally considered metabolically stressful even for adults. In the ambient CO₂ trial, oxygen concentrations reached a minimum of 4.351 µmol/L, and pH reached a minimum of 7.36. In the elevated CO₂ trial, oxygen concentrations reached a minimum of 9.910 µmol/L, and pH reached a minimum of 6.79. Flow appeared to alleviate these conditions, with highest O₂ concentrations in the egg cases exposed to 10 cm/s flow in both CO₂ trials, across all age classes measured. Surprisingly, all tested egg cases successfully hatched, demonstrating that developing D. pealeii embryos have a strong tolerance for low oxygen and pH, but there were more unsuccessful embryos counted in the 0 and 1 cm/s flow conditions. Further climate change could place young, keystone squid outside of their physiological limits, but water flow may play a key role in mitigating developmental stress to egg case bound embryos by increasing available oxygen.